1. Field of the Invention
This invention relates to gassed emulsion explosives.
2. Description of Related Art
Emulsion explosives usually consist of a water-in-oil emulsion, containing oxidisers. Historically they were manufactured with the aid of emulsifiers based on sugar esters. More recently the generic family of PIBSA (polyisobutylenesuccinicanhydride) based emulsifiers found application in this respect. PIBSA based emulsifiers result in more stable emulsions, which can be made under a wide range of process parameters, and which exhibit the required shelf life.
It is common practice in the field of emulsion explosives to manipulate the density of the explosive by controlled gassing thereof. Gassing can be accomplished by chemical or mechanical means.
Chemical gassing can be based on a number of reactions, such as the reaction of a metal with a strong acid to form hydrogen, but the most commonly used reaction is the catalytic decomposition of sodium nitrite in an acid medium to form nitrogen.
PIBSA based emulsifiers are generally able to react with the acid required for chemical gassing, usually with a deleterious effect on the emulsification properties of the emulsifier. The commonly used chemical gassing reaction can thus not be used to gas the known PIBSA based explosive emulsions.
It is also known that porous ammonium nitrate prills (PPAN), which are used in an admixture with fuel oil to form ammonium-nitrate-fuel-oil explosives (ANFO), can be stabilised with naphthalene sulphonate against the thermal degradation of the prill at 32.degree. C. Such a sulphonate is a surfactant which has an opposite emulsifying action to the emulsifiers commonly used in emulsion explosive technology. The customary admixture of ANFO, made from prills stabilised in this way, with emulsion explosives to form a product commonly known in the explosives art as "Heavy ANFO", results in the degradation of the emulsion part of the admixture and the failure of the explosive due to the incompatibility of the sulphonate and the emulsifier.